Yes, the damned Turbo Duo sound issue. I'm currently dealing with it as well, but it is on it's way to be repaired - if it is, in fact, repairable.
But there are people around here who can fix this problem for you, most notably D-Lite. You just have to take a number as this is a common problem and only a small number of people who are able to fix it. Though I guess the sound fix is one of the easier fixes, but I didn't want to risk busting my Duo even more and I was also interested in getting mods done as well.
Anyway, there's also these guys up here in Canada who will do mods/repairs (can't or won't do S-Video on the Turbo Duo yet):
http://www.oldschoolgamer.ca/information.aspx?SID=15In the end, I know your pain and so do a lot of other Turbo Duo owners. lol